This project is aimed at investigating the use of Sensory-Decision Theory in measuring sensory discriminability and response bias in experimental pain responses. The current work revealed that the indices of these two pain components, d' and B, as proposed by Clark (1971), are not completely independent; and that in an experimental condition with treatment (or analgesic drug) the estimation of change in response bias through using index B is not independent of the change in sensory discriminability before and after treatment. The sampling behavior of these two components and their changes due to treatment has been extensively investigated by simulation method. A new valid estimate of the change in response bias has been developed. The report of this study has been accepted to be presented at the Second World Congress on Pain in August 1978.